Cellulose is one of the dry matters in paper and its percentage in the paper may be measured by directing infrared light from an optical source to the paper. Interaction between the paper and the infrared light causes the attenuation of the infrared light to depend on both wavelength and the percentage of cellulose. Cellulose attenuates strongly at known, narrow absorption bands in infrared region. When an attenuation of an absorption band of cellulose is measured, it is possible to determine cellulose content of the measured paper.
When paper comprises a plurality of dry matters and lignin the amount of which is usually unknown the measurement faces serious problems and fails to provide reliable results. Hence, there is a need for a better measurement.